The present disclosure relates generally to empty-load devices of rail brake system and more specifically to empty-load devices which can be used in a pneumatic and electrically controlled pneumatic (ECP) rail brake system.
A dual-mode empty-load (EL) system is disclosed, which provides EL function in both ECP and AAR-standard pneumatic modes. As is well known, an AAR standard empty-load system operates in response to brake cylinder pressure to determine car loading by measuring spring deflection of the bogie and act to reduce the brake cylinder pressure in the empty car state by means of a proportioning valve and related empty-load displacement volume. In the loaded state, the empty-load system bypasses the proportioning valve and volume, so the full pressure of brake cylinder air is delivered to the brake cylinder.
A typical empty-load valve is New York Air Brake's EL-60 or SC-1 and U.S. Pat. No. 5,211,450 to Gayfer et al., in a single housing. Another patent to Gayfer et al., U.S. Pat. No. 6,666,528, shows the load sensing and the proportion valve being in two different housings. Both these patents are incorporated herein by reference. In each of these, an arm is used to sense the displacement between the car body and the truck as an indication of weight. For bulk commodity cars, the load sensing is through the wall of the bin wherein the contents of the car press on a membrane which is in communication with the device. This type of device is exemplified by the Beacon U.S. Pat. No. 3,960,411. A device disclosed by Beacon et al., U.S. Pat. No. 5,039,174, shows the same structure used for bulk commodity cars as well as those which measure the load by the displacement between the truck and the car body.
In ECP operation, the empty or load brake pressure regulation is provided by the ECP Car Control Device (CCD). Empty-Load status of the car is communicated electronically to the CCD alternatively as a train set-up variable input by the train driver in the controlling or lead locomotive or by means of an electronic or electro-mechanical empty-load device on each car. See for example U.S. Pat. No. 6,484,085 and U.S. Pat. No. 6,648,425. Head-end empty-load control is typically used for bulk-commodity unit trains which are either completely empty or completely full, while on-car sensors can be used for mixed freight trains and for inter-modal cars, for which the car loading may differ from car to car in the train.
Although an ECP train requires only electronic empty-load while operating in ECP mode, the system includes a pneumatic emergency brake back-up mode in the event of complete failure of the train ECP brake control. In this mode, pneumatic empty-load function is required to prevent wheel damage on empty cars by over braking. But as already described, prior art pneumatic empty-load systems regulate the output of the brake control valve, while the ECP system produces the correct pressure directly. If a prior art empty load system is installed on a car with ECP then in the empty state, the ECP would produce the correct (lower) brake pressure, and the pneumatic empty-load would further reduce that pressure by means of the aforementioned proportioning valve and volume. The result is less braking then desired.
A rail vehicle brake system according to the present disclosure includes an electrically controlled pneumatic brake valve connected to a brake pipe and having a controller connected to a network, and an empty-load device connecting the brake valve to a brake device. The empty-load device includes an inlet to receive a brake signal from the brake valve, an outlet for a brake device, a load sensing element, a change over valve for proportioning the pressure at the inlet and the outlet when empty is sensed by the load sensing element, and a differential pressure element connecting the load sensing element and the change over valve. An electro-pneumatic lock-out valve is controlled by the controller and has a first position which allows the proportioning of the inlet pressure to the outlet and a lock-out position which pneumatically prevents the proportioning of the inlet pressure to the outlet.
The controller controls the lock-out valve in responsive to an empty-load signal on the network. Alternatively, the brake system may include a sensor for sensing the vehicle load and wherein the controller is connected to the sensor and controls the lock-out valve in responsive to the sensed load. The sensor may sense the position of the load sensing element of the empty-load device. The sensor may be connected to the controller by the network. The lock-out valve and/or the sensor may be mounted to the empty-load device.
The lock-out valve may be connected in parallel to the change over valve with respect to the inlet and outlet. Alternatively, the lock-out valve may be connected in parallel to both sides of the differential pressure element. The lock-out valve is spring biased to the first position. The controller may control the lock-out valve to the lock-out position only when a brake command for an empty car is present.
In another embodiment, the rail vehicle brake system includes the electrically controlled pneumatic brake valve connected to a brake pipe and having the controller, and an empty-load device connecting the brake valve to a brake device. A sensor is connected to the controller for sensing the vehicle load; and the controller controls the brake valve in response to the sensed load taking into account the operation of the change over valve.
The sensor may sense the position of the load sensing element of the empty-load device. The load sensing element may have a stepped profile and the controller determines an empty condition or a loaded condition as a function of the steps position relative to the sensor. Alternatively, the load sensing element have a plural stepped profile or tapered profile and the controller determines the degree of load as a function of the steps or taper position relative to the sensor, wherein the travel of the load sensing element is proportional to car load.
An empty-load device includes an inlet to receive a brake signal and an outlet for a brake device. A load sensing element and a change over valve, for proportioning the pressure at the inlet and the outlet when empty is sensed by the load sensing element, is provided. A differential pressure element connects the load sensing element and the change over valve. A sensor senses the position of the load sensing element of the empty/load device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.